Determination of mobile heavy metal fraction in soil: Results of a pot experiment with sewage sludge

Abstract

The development of a method using a chelating resin to assess heavy metal mobility in soil and the first results obtained from a pot experiment with sewage sludge additions were studied. The resin was Chelex 100 with the calcium (Ca)‐form of the resin proving to be best suited for the extraction. The efficiency of recovery of the heavy metals from an aqueous solution ranged from 81.2% for cadmium (Cd) to 102% for copper (Cu) within 24 hours. For heavy metal extractions from a soil sample, a 96 hour extraction period was found to be optimum. The extracted heavy metal portion was comparable with the results obtained with an ammonium acetate (NH₄AOc) extraction. Total heavy metal contents in the substrate of the pot experiment did not show a significant influence due to the sewage sludge treatments, although considerable amounts of heavy metals were added by the sewage sludge. This effect can be both due to the incomplete recovery of heavy metals by an aqua regia extraction and leaching losses of these elements from the pots. Rape (Raphanus sativus L.) plants did not have any heavy metal contents which might indicate a high availability in soil, with the Cd and Cr contents in the rape biomass being partly lower in the sewage sludge‐treated pots than in the control plants; however, zinc (Zn) uptake slightly increased with increasing sewage sludge treatments. The Chelex 100 extraction procedure was correlated with Cd plant uptake, while the NH₄AOc extraction procedure was better related to the Zn uptake by rape plants.